Lyocell-based cellulose filament manufacturing process

Abstract

The present invention provides a viable manufacturing process for lyocell cellulose continuous filament yarn.

Description

[Technical field]

[0001] The present invention relates to the production of cellulose filament yarns. [Background technology]

[0002] Continuous filament yarns are widely used in the textile industry to produce fabrics with different characteristics compared to fabrics produced from yarns made using staple fibers. A continuous filament yarn is one in which all the fibers are continuous throughout the length of the yarn. Continuous filament yarns generally consist of 10 to 300 or more individual filaments that are all parallel to each other and parallel to the axis of the yarn when produced. The yarns are produced by extruding a solution or melt of a polymer or polymer derivative and then winding the produced yarn onto a bobbin or reel or by centrifugal winding to form a cake. Synthetic polymer continuous filament yarns are common. For example, nylon, polyester, and polypropylene continuous filament yarns are used in a variety of textiles. They are produced by melt spinning molten polymer through a spinneret with a number of holes corresponding to the number of filaments required for the yarn to be produced. After the molten polymer begins to solidify, the yarn can be pulled to orient the polymer molecules and improve the yarn properties. Continuous filament yarns can also be spun from cellulose derivatives such as cellulose diacetate and cellulose triacetate by dry spinning. The polymer is dissolved in a suitable solvent and then extruded through a spinneret. After extrusion, the solvent rapidly evaporates and the polymer precipitates into filaments that form the yarn. The newly produced yarn can also be pulled to orient the polymer molecules.

[0003] The viscose process can also be used to produce continuous filament yarns from cellulose. The cellulose is converted to cellulose xanthate by reaction with sodium hydroxide and carbon disulfide, then dissolved in sodium hydroxide solution. The cellulose solution, commonly called viscose, is extruded through a spinneret into an acid bath. The sodium hydroxide is neutralized and cellulose precipitates. At the same time, the cellulose xanthate is converted back to cellulose by reaction with acid. The newly formed filaments are pulled to orient the cellulose molecules, washed to remove reactants from the filaments, then dried and wound onto bobbins. In earlier versions of this process, the wet yarn was collected into a cake using a centrifugal winder - a Topham Box. The cake of yarn was then dried in an oven before being wound onto a bobbin. Continuous filament cellulose yarns are also produced using the Cupra process. Cellulose is dissolved in a solution of cupric ammonium hydroxide. The resulting solution is extruded into a water bath, diluting the cupric ammonium hydroxide and precipitating the cellulose. The resulting yarn is washed, dried, and wound onto bobbins. Cellulose continuous filament yarns produced by the viscose or cupra process can be made into fabrics by weaving or knitting or other fabric-forming processes. The fabrics produced are used in a variety of applications, including outerwear linings, women's blouses and tops, lingerie, and prayer rugs. Yarns are also manufactured for use in tire reinforcement and other rubber products.

[0004] Fabrics made with continuous filament cellulosic yarns can have a high luster. They have excellent moisture handling for enhanced wearer comfort. They do not generate static electricity as easily as fabrics made using continuous filament synthetic yarns. However, currently available fabrics made from continuous filament cellulose yarns generally have poor physical properties. Dry strength and tear strength are poor compared to fabrics made from synthetic polymers such as polyester. Wet strength is much lower than dry strength due to the interaction of cellulose with water. Abrasion resistance is poor. Also, interaction with water softens cellulose, making fabrics made from the yarn unstable when wet. Due to these deficiencies, products originally made using continuous filament cellulosic yarns are now primarily manufactured using synthetic polymer continuous filament yarns such as polyester and nylon.

[0005] However, synthetic yarns exhibit certain drawbacks: Fabrics made with them do not have the moisture-handling capabilities of fabrics made from cellulose yarns. Synthetic fabrics can generate static electricity. Some people consider clothing made with synthetic yarns to be much less comfortable to wear compared to cellulose-containing fabrics. Thus, there is a need for continuous filament cellulosic yarns that can be used to produce fabrics and other textile products that have the positive properties of currently available fabrics made with continuous filament cellulosic yarns, but also have the performance typically associated with fabrics made with continuous filament synthetic yarns.

[0006] Surprisingly, it has been found that continuous filament yarns produced by the Lyocell process have a significantly higher tensile strength than filament yarns produced by the Viscose process. This allows for fabrics with better strength, tear strength and abrasion resistance. The strength loss of Lyocell filaments when wet is much lower than for viscose filaments. This means that Lyocell fabrics are less prone to deformation when wet, providing better fabric stability. Also, Lyocell fabrics are stronger when wet compared to comparable viscose fabrics. It has also been surprisingly found that fabrics made from lyocell continuous filaments can have the desirable properties of luster, moisture handling, and low static build-up of continuous filament viscose and cupra fabrics.

[0007] Lyocell technology is based on the direct dissolution of cellulose wood pulp or other cellulosic raw materials in a polar solvent (e.g., N-methylmorpholine N-oxide, hereafter referred to as "amine oxide") to produce a viscous, high shear thinning solution that can be formed into a variety of useful cellulosic materials. Commercially, the technology is used to produce cellulosic staple fibers (commercially available under the trademark TENCEL from Lenzing AG, Lenzing, Austria) that are widely used in the textile and nonwoven industries. Other cellulosic products from Lyocell technology have also been disclosed, such as filaments, membranes, casings, beads, and nonwoven fabrics.

[0008] EP823945B1 discloses a process for the production of cellulose fibres, which comprises the extrusion and coagulation of a cellulose spinning solution according to the Lyocell process, which necessarily includes the steps of drawing filaments and chopping said filaments into cellulose fibres, which can be used in various fields of application. In particular, the process step of drawing the coagulated cellulose filaments is essential according to the teachings of this prior art in order to obtain staple fibres with the desired balance of properties. EP 0853146 A2 discloses a process for the preparation of cellulosic fibers. According to the teaching of this document, two different raw materials with significantly different molecular weights are mixed to obtain fibers. WO 98 / 06754 discloses a similar method, which requires that the two different raw materials are first dissolved separately before mixing the prepared solutions to obtain a spinning solution. DE 19954152 A1 discloses a method for preparing fibers, which uses a spinning solution at a relatively low temperature. The advantages of cellulose filament yarns produced from lyocell spinning solutions have been described (Krueger, Lenzinger Berichte 9 / 94, p. 49ff.). However, the prior art relating to the production of lyocell staple fibers or cellulose filament yarns via known processes does not provide a teaching of how to produce continuous filament lyocell yarns in a viable manner. Thus, the known processes suffer from the drawback that no commercially viable process is yet known, since the quality of filaments and yarns obtained by the prior art processes for forming Lyocell filaments is unsatisfactory.Furthermore, the teachings of the prior art relating to the production of fibers and filaments from other process technologies (viscose, synthetic filaments) are not applicable to the Lyocell process, since they require polymeric elongation immediately after controlled solvent removal by solution exchange following extrusion.

[0009] Thus, the preparation of continuous filament lyocell yarns presents new process challenges compared to the production of lyocell staple fibers, mainly due to much faster production speeds, filament uniformity requirements, and the need for special process continuity. Filament production rates ten times faster than staple fiber production are typical. · In continuous filament yarn products, the properties of the individual filaments must be within a very narrow band of variation to avoid problems such as variations in dye uptake. For example, the coefficient of variation of the denier distribution must be less than 5%. On the other hand, in the staple fiber process, there is a lot of room to "average out" the slight variations between the individual filaments, since each bale of fiber consists of millions of individual fibers obtained from filaments cut to required lengths and mixed. An example of Lyocell staple fiber formation is disclosed in EP823945B1. · Ultra-high purity levels of spinning solution are required to minimize filament breakage during the drawing process. Breakage can result in loss of individual filaments resulting in yarn that no longer meets the required specifications, and potentially loss of continuity of spinning. Staple fiber manufacturing processes tolerate a certain percentage of individual filament breakage. Summary of the Invention

[0010] It is therefore an object of the present invention to provide a process that allows the production of lyocell filaments and lyocell multifilament yarns with high quality and a process control that makes the entire process commercially viable.

[0011] Thus, the present invention provides a process as defined in claim 1. Preferred embodiments are set out in claims 2 to 10 and in the specification. Furthermore, the present invention provides the resulting filaments and yarns as defined in claim 11 and in the present application. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic representation of a process according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The limitations of the prior art have been overcome by the invention disclosed herein, namely, the present invention provides a process for producing lyocell filaments and lyocell multifilament yarns as defined in claim 1. The invention is described in detail with reference to individual process steps. It is understood that these process steps and corresponding preferred embodiments may be combined as appropriate, and that the present application encompasses and discloses these combinations, even if not explicitly described herein.

[0014] · Preparation of spinning solution It has been found that the known manufacturing conditions for Lyocell spinning solutions are not suitable for the production of Lyocell continuous filaments. In order to achieve the required performance and product uniformity and consistency, it is necessary to use a cellulosic starting material that meets the following requirements:

[0015] The rheological properties of known lyocell spinning solutions are not adapted to the requirements of high speed filament yarn production. For example, when using known spinning solution compositions in staple fiber production, an unacceptable number of filament breaks occurs. It has been found that this problem can be overcome by using a cellulose raw material with a broader molecular weight distribution than those disclosed so far, i.e. by blending 5-30% by weight, preferably 10-25% by weight, of cellulose having a scan viscosity in the range of 450-700 ml / g with 70-95% by weight, preferably 75-90% by weight, of cellulose having a scan viscosity in the range of 300-450 ml / g, when these two fractions have a scan viscosity difference of more than 40 ml / g, preferably more than 100 ml / g. The scan viscosity is determined in caprylethylenediamine solution according to SCAN-CM 15:99, a technique known to the skilled person and which can be carried out on commercially available equipment such as the Auto PulpIVA PSLRheotek equipment from psl-rheotek.

[0016] To obtain such cellulose raw materials (e.g., from wood pulp) to achieve the required molecular polydispersity, blends of different types of starting materials may be used. The optimal blend ratio will depend on the actual molecular weight of each blend component, the filament manufacturing conditions, and the specific product requirements of the filament yarn. Alternatively, the required cellulose polydispersity can be obtained, for example, by blending during the wood pulp manufacturing process before drying. This eliminates the need for careful monitoring and blending of pulp stocks during lyocell manufacturing.

[0017] The total content of cellulose in the spinning solution is typically 10-20% by weight, preferably 10-16% by weight, such as 12-14% by weight. A person skilled in the art will recognize the components required for the spinning solution for the Lyocell process, and therefore further detailed description of said components and general manufacturing methods is not considered necessary here. See U.S. Pat. No. 5,589,125, WO 96 / 18760, WO 02 / 18682, and WO 93 / 19230, which are incorporated herein by reference.

[0018] To further control the process according to the invention, a high level of process monitoring and control is preferably used to ensure uniformity of the composition of the spinning solution, which may include in-line measurement of spinning solution composition / pressure / temperature, in-line measurement of particle content, in-line measurement of spinning solution temperature distribution in the jet / nozzle, and periodic offline cross-checks.

[0019] It is further preferred to control and, if necessary, improve the quality of the lyocell spinning solution used in the present invention, since the inclusion of large particles can result in unacceptable breakage of individual filaments during the formation process. Examples of such particles are impurities, such as sand, and gel particles containing insufficiently dissolved cellulose. One option for minimizing the content of such solid impurities is a filtration process. Multi-stage filtration of the spinning solution is the optimal method for minimizing solid impurities. Those skilled in the art will understand that for finer filament finenesses, higher filtration stringency is required. Typically, for example, a deep bed filtration with an absolute stopping power of about 20 microns has been found to be effective for 1.3 decitex filaments. For finer filament decitex, an absolute stopping power of 15 microns is preferred. The equipment and process parameters for carrying out the filtration are known to those skilled in the art. In addition, it has been found that it is appropriate to adjust the viscosity of the spinning solution to a range of 500 to 1350 Pa·s, measured at 110° C. and a shear rate of 1.2 (1 / s).

[0020] The temperature of the spinning solution during its preparation is typically in the range of 105-120°C, preferably 105-115°C. Before the actual spinning / extrusion, the solution is heated, optionally after filtration, to a higher temperature, typically 115-135°C, preferably 120-130°C, using processes and equipment known to those skilled in the art. This process, together with the filtration step, increases the homogeneity of the spinning solution after its initial preparation in order to provide the spinning solution (sometimes called spin) suitable for extrusion through a spinning nozzle. The spinning solution is then preferably brought to a temperature of 110°C-135°C, preferably 115°C-135°C, before extrusion / spinning, a process which may include intermediate cooling and heating stages, as well as a tempering stage (where the spinning solution is maintained at a given temperature for a certain time). Such processes are known to those skilled in the art.

[0021] Filament extrusion It has been found that a uniform and constant flow rate of the spinning solution through each spinneret nozzle hole further improves the process and helps to meet the quality requirements for the individual cellulose filaments and, as a result, for the multifilament yarn. This is particularly relevant in view of the very high production speeds required for filament and filament yarn production, which are in the range of 200 m / min or more. According to the invention, production speeds of 200 m / min or more can be achieved, such as 400 m / min or more, preferably 700 m / min or more, even up to 1000 m / min or more. Suitable ranges are 200-1500 m / min, such as 400-1000 m / min or 700-1000 m / min, including ranges such as 700-1500 m / min.

[0022] Each spinneret section used to extrude the lyocell spinning solution has a number of nozzle holes corresponding to the number of filaments required in the continuous filament yarn. Multiple yarns can be extruded from a single jet by combining multiple spinneret sections into a single spinneret plate, as disclosed, for example, in WO 03014429 A1, which is incorporated herein by reference.

[0023] The number of nozzle holes for each filament yarn may be selected depending on the intended yarn type, but said number is typically in the range of 10-300, preferably 20-200, such as 30-150.

[0024] The uniformity of the spinning solution flow rate can be improved by providing good temperature control within the spinneret and the individual nozzles. Temperature variations within and between the nozzles during spinning should be as small as possible, preferably within ±2°C. This can be achieved by means of direct heating of the spinneret and the individual nozzles in a series of different zones, making it possible to offset any local differences in the temperature of the spinning solution and to precisely control the temperature of the spinning solution as it is extruded from each spinneret nozzle. Examples of such temperature control means are disclosed in WO 02 / 072929 and WO 01 / 81662, which are incorporated herein by reference.

[0025] The spinneret nozzle profile is preferably designed to maximize the smooth acceleration of the spinning solution through the nozzle while minimizing pressure loss. Important design features of the nozzle include, but are not limited to, a smooth inlet surface and sharp edges at the nozzle exit.

[0026] ·Initial cooling After leaving the spinning nozzle, the individual filaments are typically subjected to a cooling process, typically using air flow. Thus, the cooling of the filaments in this step is preferably performed by using a draught, preferably a controlled cross draught in an air gap. The draught should have a controlled humidity to obtain the desired cooling effect without adversely affecting the fiber quality. Suitable humidity values ​​are known to those skilled in the art. However, a direct application of the known Lyocell staple fiber procedure to this step does not work well, since it requires a very long air gap (more than 200 mm) taking into account the high filament production speed. However, such an air gap is not feasible, since the individual filaments move and come into contact, leading to filament fusion and poor product quality. For the same reason, it has been found that high speed cross draughts disclosed for staple fiber production can also present problems. In addition, for filament products, a higher uniformity and consistency of drawing is required compared to staple fibers.

[0027] The present invention therefore provides a novel means of adjusting the filament production process in order to meet the quality requirements of filament yarn production.

[0028] Suitable cross-ventilation mechanisms are disclosed, for example, in WO 03014436 A1, which is incorporated herein by reference.Uniform filament cooling over the length of the air gap is preferred.

[0029] As outlined above, the long air gaps considered necessary according to the general spinning process understanding, especially when considering high production speeds, are not feasible. However, it has been found that longer air gap lengths than are typically used in staple fiber production, such as about 40-130 mm, can be used successfully. Preferably, the air gap is in the range of 40-120 mm, such as 50-100 mm. In an embodiment, this can be combined with increased filament spacing at the spinneret face (about twice the nozzle spacing used in Lyocell staple fiber production). Such a mechanism has been found to be beneficial for filament production. Increasing the filament spacing in this way reduces the possibility of filaments touching and allows the required uniform filament cooling to be achieved.

[0030] The cross air speed is preferably much lower than that used in Lyocell staple fiber production. Suitable values ​​are 0.5-3 m / s, preferably 1-2 m / s. Humidity values ​​may be in the range of 0.5-10 g water / kg air, such as 2-5 g water / kg air. The air temperature is preferably controlled at a value below 25°C, such as below 20°C.

[0031] Initial solidification of the filament After leaving the spinneret nozzle and being cooled in the air gap, the produced filaments need to be further processed for initial solidification. This is achieved by placing the individual filaments in a coagulation bath, also called spin bath. In order to achieve a high degree of product quality uniformity, it has been found that this further initial solidification of the filaments is preferably carried out within narrow tolerances, i.e. with only slight variations, preferably at precisely the same position. It has been found that conventional spin bath designs are often not suitable for this purpose, since the fluid forces resulting from high filament speeds (greater than about 400 m / min) disrupt the bath surface, resulting in non-uniform initial solidification (and variable air gap size), and even possible filament fusion and other damage. To address such issues, it has been identified that it is preferable to use a shallow spin bath having a depth of less than 50 mm.

[0032] Such spin baths are disclosed, for example, in WO 03014432 A1, which is incorporated herein by reference, and which discloses shallow spin bath depths in the range of 5 to 40 m, preferably 5 to 30 mm, and more preferably 10 to 20 mm. The use of such shallow spin baths allows for control of the contact position of the spun filaments with the coagulation solution in the spin bath, thereby avoiding the problems that may occur when using conventional spin bath depths.

[0033] In addition, it has been found that filament quality can also be improved if the concentration of amine oxide in the spin bath is controlled to a value lower than that typically used for lyocell fiber production. Spin bath concentrations of less than 25% by weight, more preferably less than 20% by weight, and even more preferably less than 15% by weight, have been found to improve filament quality. A preferred range of amine oxide concentration is 5-25% by weight, such as 8-20% by weight or 10-15% by weight. This is significantly lower than the ranges disclosed for lyocell staple fiber production. To be able to maintain such low amine oxide concentrations, continuous monitoring of the composition of the spin bath is preferred, whereby, for example, adjustment of the concentration can be made by water replenishment and / or by selective removal of excess amine oxide. The temperature of the spin bath is typically within the range of 5 to 30°C, preferably 8 to 16°C.

[0034] Similar to the preferred embodiment disclosed above for the spinning solution, high stringency spin bath solution filtration is contemplated to minimize the possibility of damage to the delicate freshly formed filaments by undesirable solid impurities in the spin bath, which is especially important for very high production speeds of over 700 m / min.

[0035] Within the spin bath, the individual filaments of the desired final yarn are brought together and bundled into an initial multifilament bundle by an outlet from the spin bath, typically a ring-shaped outlet, which serves to bring the filaments together and also to control the amount of spin bath solution that leaves the bath together with the filament bundle. Suitable mechanisms are known to those skilled in the art. Since at least a portion of the filaments come into contact with the ring-shaped outlet, the shape and even the choice of material of the ring-shaped outlet influences the tension on the filament bundle. Those skilled in the art will know suitable materials and shapes for these outlets from the spin bath to minimize any negative effects on the filament bundle.

[0036] Thus, in a preferred embodiment of the process according to the invention, said process comprises the step of producing a spinning solution suitable for the Lyocell process containing 10-15% by weight, preferably 12-14% by weight, of cellulose, said cellulose being the above-mentioned blend of celluloses having different scan viscosity values. The process further comprises the step of extruding said spinning solution through an extrusion nozzle, while maintaining a temperature variation through said extrusion nozzle of less than ±2° C. The filaments thus produced are subjected to an initial cooling as described above, followed by said initial solidification of the filaments thus obtained in a coagulation bath (spinning bath) having a depth of less than 50 mm, preferably between 5 and 40 mm, more preferably between 10 and 20 mm.

[0037] The composition of the coagulation liquid used in the coagulation bath exhibits an amine oxide concentration of less than or equal to 23% by weight, more preferably less than 20% by weight, even more preferably less than 15% by weight. Control of the amine oxide content can be achieved by adjusting the concentration to the preferred range by selective removal of amine oxide and / or by supplementation with fresh water.

[0038] Such a process ensures the production of high quality and particularly high uniformity filaments, which are introduced into the coagulation bath in a manner that ensures in particular uniform coagulation and therefore uniform filament properties. In addition, in the above-mentioned process embodiments, it is preferred to adjust the distance between the individual filaments during extrusion, for example by using a wider nozzle spacing, as compared to standard Lyocell staple fiber production processes, as described further below. These preferred process parameters and conditions allow the production of Lyocell filaments with high uniformity, as described herein, while at the same time allowing the desired high process speeds (spinning speeds of 200 m / min or more, more preferably 400 m / min or more, and in embodiments as high as 700 m / min or more). In this context, the present invention further allows the continuous and long-term production of cellulose Lyocell filaments and corresponding yarns, since the above-mentioned process parameters and conditions avoid filament breaks and the like that would require the production of filaments and yarns to be stopped.

[0039] Filament drawing After leaving the spinning bath, the multifilament bundle is typically taken up by guide rollers that direct the bundle to the next processing stage, such as washing, drying and winding, resulting in the final yarn. During this step, preferably, no stretching of the filament bundle is performed. The distance from the exit of the spinning bath to the contact with the guide rollers may be selected as required, a distance of 40-750 mm, such as 100-400 mm, has been shown to be suitable. It has been found that this process step can provide further options for controlling and influencing product quality. In this process step, for example, the crystal structure of the filaments can be adjusted, thereby achieving the desired properties of the lyocell continuous filament yarn. As stated above and as can be derived from the wording of claim 1, it has been found that the success of this process step is closely related to the rheology of the spinning solution and the consistency of extrusion from the nozzle, as stated above.

[0040] As mentioned above, means such as guide rollers take up the filaments and gather them to form an initial yarn, which is then guided towards further processing steps. According to the present invention, the maximum tension applied to the filament bundle (yarn) at the contact point between the filament bundle and the guide rollers is (4.2 x number of filaments / filament fineness) 0.69 It is preferable that the tension is equal to or less than 4.2×60:1.33. This tension means the tension applied to the filament / filament bundle from the position where it leaves the spinning nozzle to the position of first contact, for example, to the position of first contact with the guide roller provided after the coagulation step. From the formula provided above, as an example, the maximum tension for a filament bundle having, for example, 60 filaments and a yarn fineness of 80 dtex (each filament has a fineness of 1.33 dtex) is determined, and the maximum tension is (4.2×60:1.33) 0.69 , therefore 37.3cN.

[0041] By maintaining such a specific maximum tension, it is possible to ensure that filament breakage is prevented so that high quality yarn can be obtained. In addition, this helps to ensure that the filament production process can continue for the required time without failure. Those skilled in the art will understand that the tensions referred to herein are tensions measured using samples taken from the entire process by using a three roll testing apparatus Schmidt-Zugspan-nungsmessgerat ETB-100. The tensions measured on the filaments and filament bundles at the designated contact positions referred to herein can be used to control product quality and process stability by adjusting the process parameters disclosed herein with respect to the present invention, in particular the composition of the spinning solution, the spinning bath depth and the spinning bath liquid (coagulation bath) composition, the cross draft, and spinneret design such as nozzle design and nozzle spacing, in order to adjust the tension values ​​to values ​​according to the formula provided above.

[0042] Cleaning the filament Since the filaments after initial solidification and cooling still contain amine oxide, the resulting filaments and / or yarns are typically subjected to washing. Amine oxide can be removed from the newly formed yarns via countercurrent flow of demineralized water or other suitable liquid, typically at 70-80°C. As with the previous process steps, it has been found that conventional washing methods, e.g., the use of troughs, can present problems in view of high production speeds, exceeding about 400 m / min. In addition, uniform application of washing liquid to each individual filament is preferred to obtain a high quality product. At the same time, it is also preferred that there is minimal contact between the sensitive filaments and the washing surface, with the aim of maintaining the integrity of the filaments to achieve the desired yarn properties. Furthermore, individual filament yarns need to be washed in close proximity to each other, and line lengths should be minimized to make the process economically viable. In view of the above, it has been found that a preferred washing process includes the following, either alone or in combination:

[0043] Washing is preferably carried out using a series of driven rollers, with each yarn being individually subjected to a series of wash impregnation / wash removal steps.

[0044] It has been found to be beneficial to provide a means for uniformly removing or de-liquifying liquid from each yarn filament after each wash impregnation step without damaging the sensitive filaments. This can be achieved, for example, via appropriately designed and positioned pin guides. The pin guides may be constructed, for example, of a matte chrome finish. The guides allow for close spacing of the filament yarns (approximately 3 mm), good contact with the filaments, resulting in uniform liquid removal and low tension to minimize filament damage.

[0045] Optionally, an alkaline wash step may be included to enhance the efficiency of removing residual solvent from the filaments.

[0046] The spent wash solution (after the first pin guide) typically has an amine oxide concentration of 10-30%, preferably 18-20%, before being returned to solvent recovery.

[0047] A "softener" may be applied to aid in further processing. Types and methods of application are known to those skilled in the art. For example, it has been found effective to apply about 1% of the finish onto the filaments with a "lick-roller" mechanism, followed by nip rollers to control the tension of the yarn going to the dryer.

[0048] Drying the yarn Again, good control of this process helps develop optimal yarn properties and minimizes the possibility of filament damage. Drying means as well as drying parameters are known to those skilled in the art. Preferred embodiments are defined below.

[0049] The dryer may consist of, for example, 12-30 heated drums of about 1 m diameter. It is preferable to control the individual speeds to ensure that the tension in the filaments remains low and constant, preferably less than 10 cN, preferably less than 6 cN. The spacing of the yarns throughout the drying process may be about 2-6 mm.

[0050] The initial temperature of the dryer is about 150° C. In later stages of the drying process the temperature can be lower as drying progresses.

[0051] After drying, antistatic agents and / or fabric softeners may be applied to the filament yarn by means known to those skilled in the art.

[0052] Further process steps, such as yarn blending, bulking, interweaving, may be applied after drying and before collection using processes known to those skilled in the art. If desired, a fabric softener may be applied to the yarn prior to the steps indicated above.

[0053] -Yarn collection The yarn may be collected using standard winding equipment. A suitable example is a single-line winder. The winder speed is used to fine-tune the upstream process speed to maintain a low and constant yarn tension.

[0054] Those skilled in the art will understand that various modifiers, such as dyes, antimicrobial products, ion exchange products, activated carbon, nanoparticles, lotions, flame retardant products, superabsorbents, impregnating agents, dyes, finishing agents, crosslinking agents, grafting agents, binders, and mixtures thereof, may be added during the preparation of the spinning solution or in the washing zone, provided that the addition does not inhibit the spinning process. This allows the filaments and yarns produced to be modified to meet individual product requirements. Those skilled in the art are well aware of how to add such above-mentioned substances during the steps of the lyocell filament yarn production process. In this regard, it has been found that many desirable modifiers that would normally be added in the washing stage are not effective in the filament yarn path due to the high line speed and therefore short residence time. Another alternative approach to introduce these modifiers is to recover the well-washed but "not dried at all" filament yarns and subject them to further processing in batches, where residence time is not a limiting factor.

[0055] An exemplary process according to the present invention is described with reference to FIG. 1. In FIG. 1, item (1) denotes a spinneret with numeral (2) indicating the spinning hole (nozzle) from which each filament (3) is extruded. The vessel containing the spinning solution and preceding steps such as a filtering step are not shown in FIG. 1, but a person skilled in the art would understand how the spinning solution enters the spinneret. Number (4) denotes a precipitation or coagulation bath, and further numeral (5) denotes the surface of the coagulation bath. As shown herein, each filament (3) exiting the spinneret is guided to a coagulation bath and exits from the coagulation bath according to standard procedures. Each filament is then taken up by guide rollers to form a bundle of filaments (14) that ultimately forms a multifilament yarn according to the present invention. Number (7) denotes the first contact location of the bundle of filaments (14) with the guide roller (6). According to the description herein, a maximum tension applied to the bundle of filaments between the induced first contact location (7) and the end of the spinhole (2) is preferably defined herein, such maximum tension ensuring the production of high quality filaments and yarns while maintaining process conditions to allow stable long-term production of multifilament yarns. The bundle of filaments (14) is then guided to a washing treatment (8), an optional post-treatment facility (9), followed by a drying facility (10), which may include various heated drums (11a, 11b, 11c) resulting in a dried multifilament yarn (14a) exiting the drying facility. As mentioned above, the drying is preferably carried out to ensure a constant and fairly low filament tension of 10 cN / 80 dtex or less. According to the above, high quality multifilament yarns can be produced in a reliable and commercially viable manner.

[0056] According to the process described herein, cellulose filaments and yarns can be produced that are lyocell filaments and yarns. The properties of the produced filaments and yarns can be adjusted according to the respective requirements for the desired end use, such as the number of filaments per yarn, the tighter filaments, the total yarn fineness, other properties of the filaments and yarns. The following example further illustrates the process.

[0057] Pulp (cellulose) was impregnated with 78% aqueous N-methylmorpholine N-oxide (NMMO) solution and a small amount of stabilizer. The resulting suspension contained 11.6% cellulose, 67.8% NMMO, 20.6% water, and stabilizer GPE. The pulp consisted of a mixture of 80% with a viscosity of SCAN 350 ml / g and 20% with a viscosity of SCAN 600 ml / g. Excess water was removed from the slurry under shear and heat to obtain a fiber-free cellulose solution containing 13% cellulose, 73.8% NMMO, and 11.2% water. The cellulose solution was filtered and conditioned to obtain a spinning solution, which was extruded at 112°C in a wet-dry process, where the spinning solution was extruded through a nozzle into a 60mm high air gap, where a conditioned air flow of 2.5m / s, 2g water per kg air, and 17°C was provided to stabilize the extrusion process. After passing through the air gap, cellulose was precipitated in a 24 mm high initial spin bath containing 12% NMMO and the remainder water at a filament tension of 27 cN. The endless filaments so obtained were washed with water, impregnated with a finish, dried and wound on bobbins. Washing was carried out in countercurrent with fully demineralized water at 50°C with 25 wash cycles. For drying, a contact drum dryer was used with three temperature zones (155°C / 140°C / 100°C) and the humidity was reduced to 10.5%. The tension of the filament bundle was 17 cN. The spinning speed was 500 m / min.

Claims

1. 1. A process for producing lyocell-based cellulose filament yarns from a lyocell spinning solution of cellulose in an aqueous solution of a tertiary amine oxide, comprising: a) preparing a spinning solution containing 10-20 wt. % cellulose, said cellulose being a blend of 10-25 wt. % cellulose having a scan viscosity in the range of 450-700 ml / g and 75-90 wt. % cellulose having a scan viscosity in the range of 300-450 ml / g, said two fractions exhibiting a scan viscosity difference of 40 ml / g or more; b) extruding the spinning solution through an extrusion nozzle to obtain filaments; c) initially coagulating the filaments with a spin bath containing a coagulation liquid having a concentration of tertiary amine oxide of 20% or less; d) washing the filaments; e) drying the filaments; Including, A gap in the range of 40 to 130 mm is provided between the outlet of the nozzle and the surface of the spinning bath; The spinning bath has a depth of 5 to 30 mm. process.

2. 10. The process of claim 1 for producing a multifilament yarn.

3. The process of claim 1 or claim 2, wherein the filaments after exiting the nozzle are contacted with a cross-draft airflow of 0.5 to 3 m / sec.

4. The process according to any one of claims 1 to 3, wherein the filaments are taken up by guide rollers after exiting the spin bath.

5. The maximum tension applied to the bundle of filaments at the contact position between the bundle of filaments and the guide roller is (4.2 x number of filaments / filament fineness). ０．６９ (c 5. The process of claim 4, wherein the number of ions is equal to or less than N.

6. The process according to any one of claims 1 to 5, wherein in step e) the drying is carried out at a constant filament tension of less than 10 cN per 80 dtex.

7. A process according to any one of claims 1 to 6, wherein the temperature variation through the extrusion nozzle is controlled to no more than ±2°C.

8. The process of claim 1, further comprising washing the yarn.

9. The process according to any one of claims 1 to 8, wherein the spinning solution is subjected to a filtration step prior to filament formation.

10. 10. The process according to any one of claims 1 to 9, wherein the concentration of tertiary amine oxide in the spinning bath is 8 to 20% by weight, and / or an air gap in the range of 50 to 100 mm is provided between the outlet of the nozzle and the surface of the spinning bath, and / or the spinning bath has a depth of 10 to 20 mm, and / or the spinning solution has a temperature of 105 to 120°C, and / or a cross draft of air having a speed of 0.5 to 3 m / s is provided in the air gap.

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